Conventionally, as a writing implement having a reverse flow prevention mechanism for ink, for example, a ballpoint pen disclosed in JP 04-52067 Y or JP 3197422 B is known. Hereinafter, explanation is made referring to both FIG. 8 illustrating the former prior art and FIG. 9 illustrating the latter one. Here, the figures referred to in the following explanation are all described in these FIGS. 8 and 9.
A ballpoint pen 100 disclosed in JP 04-52067 Y, as illustrated in FIG. 8, comprises an ink storage tube 110, a joint 120 fixed to a front end of the ink storage tube 110, and a tip 130 fixed to a front end of the joint 120.
In a center of the joint 120 is provided a valve chamber 121. In front of the valve chamber 121 is provided a tip fixing hole 122 penetrating from the valve chamber 121 to the front end of the joint 120. In rear of the valve chamber 121 is provided an ink storage tube fixing hole 123 penetrating from the valve chamber 121 to a rear end of the joint 120.
At a rear part of the valve chamber 121 is provided a valve seat 124. On an inner surface of a front part of the valve chamber is provided a plurality of protrusions 125 protruding inward of the valve chamber 121.
The joint 120 is molded integrally of elastically deformable resin composition.
In the valve chamber 121 is stored a spherical valve element 126. The valve element 126 can move in the valve chamber 121 by its own weight and cannot slip out of the valve chamber 121.
A rear end part of the tip 130 is pressed into and fixed to the tip fixing hole 122. A front end of the ink storage tube 110 is pressed into and fixed to the ink storage tube fixing hole 123.
When the tip 130 is faced upward, the valve element 126 falls toward the ink storage tube 110 by its own weight and touches a whole circumference of the valve seat 124. Thereby, reverse flow of ink is prevented.
On the other hand, when the tip 130 is faced downward, the valve element 126 falls toward the tip 130 by its own weight and is caught by the protrusions 125. Thereby, the ink is supplied to the tip 130 through gaps between the protrusions 125.
On the other hand, a ballpoint pen 100 disclosed in JP 3197422 B, as illustrated in FIG. 9, comprises an ink storage tube 110, a joint 120 fixed to a front end of the ink storage tube 110, and a tip 130 fixed to a front end of the joint 120.
In a center of the joint 120 is provided a valve chamber 121. In front of the valve chamber 121 is provided a tip fixing hole 122 penetrating from the valve chamber 121 to the front end of the joint. In rear of the valve chamber 121 is provided a guiding hole 127 penetrating from the valve chamber 121 to a rear end of the joint.
At a rear part of the valve chamber 121 is provided a valve seat 124.
In the valve chamber 121 is stored a spherical valve element 126. The valve element 126 can move in the valve chamber 121 by its own weight and cannot slip out of the valve chamber 121.
A rear end of the tip 130 is pressed into and fixed to the tip fixing hole 122.
A rear end of the joint 120 is pressed into and fixed to a front end of the ink storage tube 110.
An intervening piece 140 is inserted forcibly and fixed between the valve element 126 and the rear end of the tip 130. At a rear end of the intervening piece 140 is provided ink grooves 141. Ink can pass through the ink grooves 141 when the valve element 126 touches the rear end of the intervening piece 140.
In the tip 130 is stored a spring 150. A rear end of the spring 150 touches a front end of the intervening piece 140. A front end of the spring 150 touches a rear end of a ball 131 held by a front end of the tip 130.
When writing is not performed, the ball 131 is pressed onto an inner surface of a bent portion by being pushed by the spring 150.
When the tip 130 is faced upward, the valve element 126 falls toward the ink storage tube 110 by its own weight and touches a whole circumference of the valve seat 124. Thereby, reverse flow of the ink is prevented.
On the other hand, when the tip 130 is faced downward, the valve element 126 falls toward the tip 130 by its own weight and touches the rear end of the intervening piece 140. Under this condition, the ink is supplied to the tip 130 through the ink grooves 141. Moreover, though writing is not performed, a direct flow of the ink is prevented since the ball 131 is pressed onto the inner surface of the bent portion by being pushed by the spring 150.
However, as disclosed in JP 04-52067 Y, when the protrusions are provided on the inner surface of the valve chamber, a mold structure for molding becomes rather complex since the protrusions make undercuts. Thereby, manufacturing cost for a whole writing implement becomes rather expensive. Moreover, since the protrusions make undercuts, the size of each protrusion must be made as small as possible. Then, passages for the ink flow may not be sufficiently secured depending upon a diameter of the ball or a kind of the ink.
Moreover, as disclosed in JP 319422 B, when the intervening piece is fixed between the valve element and the rear end of the tip, a shape of the intervening piece becomes complex and highly-developed manufacturing technology is necessary for a process of inserting the intervening piece into the joint with the intervening piece correctly directed. Namely, very highly-developed manufacturing technology is necessary for a process of inserting the intervening piece to be located in a predetermined position in the joint with the ink grooves of the intervening piece being directed backward. Thus, manufacturing cost for a whole writing implement becomes expensive.
Then, the first problem to be solved by the present invention is to provide a writing implement wherein elements (a valve chamber, etc.) forming a reverse flow prevention mechanism are formed in rather simple shapes and assembly process for the reverse flow prevention mechanism is rather simplified, thereby contributing to reduction of the manufacturing cost.
Moreover, the second problem to be solved by the present invention is, in addition to the first problem, to provide the writing implement wherein the assembly process for the reverse flow prevention mechanism is more simplified.